move constant folding code into an own file
be robust against multiple exit_preprocessor() calls
move constant folding code into an own file
Move posix/win32 hacks to a separate header file
refactoring of main.c
move help strings from main.c to help.c
start working on moving option parsing out of main
further moving of options to options.c
move timing and statev to options.c
move preprocessor initialisation to driver.c
introduce system for one-shot actions
move driver initialisation to driver.c